Not able to receive an attachment from Skype in BotFramework - node.js

Question

On BotFramework (NodeJS), I was trying to replicate the demo available at https://learn.microsoft.com/en-us/bot-framework/nodejs/bot-builder-nodejs-send-receive-attachments . It actually works well.
Code in case ms article change:
// Create your bot with a function to receive messages from the user
var bot = new builder.UniversalBot(connector, function (session) {
var msg = session.message;
if (msg.attachments && msg.attachments.length > 0) {
// Echo back attachment
var attachment = msg.attachments[0];
session.send({
text: "You sent:",
attachments: [
{
contentType: attachment.contentType,
contentUrl: attachment.contentUrl,
name: attachment.name
}
]
});
} else {
// Echo back users text
session.send("You said: %s", session.message.text);
}
});
However, the problem I am facing is that when I do a call from Skype (Normal), I receive an error message:
2017-12-07T02:16:15.815Z Error: POST to 'https://smba.trafficmanager.net/apis/v3/conversations/<My Conversation>/activities' failed: [400] Bad Request
at Request._callback (/app/node_modules/botbuilder/lib/bots/ChatConnector.js:545:46)
at Request.self.callback (/app/node_modules/request/request.js:186:22)
at emitTwo (events.js:126:13)
at Request.emit (events.js:214:7)
at Request.<anonymous> (/app/node_modules/request/request.js:1163:10)
at emitOne (events.js:116:13)
at Request.emit (events.js:211:7)
at IncomingMessage.<anonymous> (/app/node_modules/request/request.js:1085:12)
at Object.onceWrapper (events.js:313:30)
at emitNone (events.js:111:20)
Any ideas?
[Update: It happens only when I create the attachment response. So I expect that's where I have an issue]

Answer 1

Actually the code on the MS Website is not up-to-date (in a way).
If I follow the code visible at : https://github.com/Microsoft/BotBuilder-Samples/tree/master/Node/core-ReceiveAttachment
By example, I can receive the attachment and save it somewhere on a public folder. Once completed, then I can send back the "public" URL as attachment and then it works.